Tunable lambda/4 filter subassembly

ABSTRACT

The invention relates to a tunable λ/4-filter subassembly ( 10 ) whose frequency response can be adjusted. For this purpose, the λ/4-filter subassembly ( 10 ) has a signal-conducting electrical conductor ( 20 ) and an electrically conductive element ( 30 ) that is at a reference potential. Furthermore, at least one short-circuit device ( 40; 140 ) is provided that electrically contacts the electrical conductor ( 20; 120 ). An electrical coupling device ( 70; 170 ) is provided that couples the short-circuit device ( 40; 140 ) at a settable contact position ( 80; 180 ) to the electrically conductive element ( 30; 130 ), wherein the electrical coupling device ( 70; 170 ) and the short-circuit device ( 40; 140 ) are movable relative to each other in order to set the length of the short-circuit device ( 40; 140 ).

The invention relates to a tunable λ/4 filter subassembly with a signalconducting electrical conductor and an electrically conductive elementwhich is at a reference potential and that may be in particular, ahousing connected to ground.

λ/4-filters are used, for example, in high frequency technology asbandpass filters. Such filters have, for example, a short-circuit lineof fixed length between a signal-conducting conductor and a ground. Thebandwidth of the filter depends on the length of the short-circuitconductor, which determines the center frequency of the filter accordingto the equation f₀=c/λ. The bandpass character of such a filter isobtained from the special wave characteristic at high frequencies,since, at high frequencies, the short-circuit at the center frequency f₀is blocked, so that signals with frequencies that are distributed over acertain bandwidth about the center frequency can pass through theconductor.

Such filters are also used for surge protection, for example, in mobiletelephony.

Thus, for example in DE 9422 171 U1 describes a surge voltage protectionplug connector for a coaxial cable having an inner and an outerconductor, where a spiral-shaped short-circuiting stub of fixed lengthshort circuits the inner conductor with the outer conductor.

From U.S. Pat. No. 6,061,223, for example, a surge voltage protectiondevice is known, in which an inner conductor is arranged in a housing,which together form a coaxial line. A spiral-shaped conductor of fixedlength is used as a short-circuit element to transfer the energy duringa surge voltage event to a ground connection.

One drawback of the mentioned filter is that, due to the fixedshort-circuit length, the center frequency is determined in a fixed way.A different filter therefore must be used for each different frequencybehavior.

The present invention is therefore based on the problem of providing aλ/4-filter subassembly, which is universally usable for a variablefrequency range.

The main idea of the invention is to provide a tunable λ/4-filter, whosefrequency response is modifiable by setting the length of ashort-circuit device.

The technical problem is solved by a tunable λ/4-filter component, whichpresents a signal conducting electrical conductor and an electricallyconductive element at a reference potential. In addition, at least oneshort-circuit device is provided that establishes electrical contactwith the electrical conductor. Furthermore, an electrical couplingdevice is provided, that couples the short-circuit device at a settablecontact position to the electrically conductive element, where theelectrical coupling device and the short-circuit device are relativelymovable in order thereby to set the length of the short-circuit device.

The length of the short-circuit device is preferably continuouslyadjustable over a predeterminable length range, so that the centerfrequency of the tunable λ/4-filter subassembly also continuouslyadjustable. In this way, a λ/4-filter with variable bandpass behaviorcan be realized.

A short-circuit device advantageously has a first contact section, whichis connected to the electrical conductor, as well as a second contactsection that is connected to the first contact section and with whichthe electrical coupling device engages electrically.

A compact construction with a wide setting range is obtained if thesecond section of the short-circuit device forms an essentially circularconductor element, which is arranged essentially concentrically to andat a distance r from the electrical conductor, and whose circumferenceis less than 2 πr.

The electrical element is preferably an electrically conductive housing,which at least partially surrounds the conductor and the at least oneshort-circuit device. The housing is preferably cylindrical in design.

To be able to set the length of the short-circuit device, the couplinginstallation presents a first rotatable, electrically-conducting settingelement with a contact element. The contact element engages at asettable contact position on the short-circuit device. For this purpose,a slot of predetermined length is provided in the housing, which allowsthe contact element to be shifted with the aid of the setting elementalong the short-circuit device. The setting element is applied againstthe housing and is thus at the potential of the housing.

To be able to increase the bandwidth of the λ/4-filter subassembly, atleast one additional short-circuit device is provided, which is axiallyoffset with respect to the longitudinal axis of the electrical conductoropposite the first short-circuit device. It presents a first contactsection, which is connected to the electrical conductor, as well as asecond contact section that is connected to the first contact sectionand with which the coupling device engages electrically. In this way,the λ/4-filter subassembly has two center frequencies, which increaseits bandwidth.

To obtain a compact construction, the second contact section of theadditional short-circuit device as well forms a circular conductorelement, which is arranged essentially concentrically to and at adistance r from the electrical conductor, and whose circumference isagain less than 2 πr. The electrical element is again designed as aconductive housing that at least partially surrounds the conductor andthe short-circuit devices.

In this case, the coupling device presents a second rotatableelectrically-conductive setting element with a contact element. Thecontact element engages at a settable contact position on the secondshort-circuit device, where, in the housing, a slot is provided to shiftthe contact element. The setting element is again located outside of thehousing, so that the setting element and the housing are at the samepotential. If the housing has a circular cross section, the settingelements are annular in design.

According to an embodiment, the two setting elements can be connected toeach other. However, to be able to adjust the length of the twoshort-circuit devices individually, the two setting elements are movableindependently of each other.

To be able to change the bandwidth of the λ/4-filter, an additionalshort-circuit device located in the same plane as the firstshort-circuit device is provided according to an alternative embodiment.The additional short-circuit device presents a first contact section,which is connected to the electrical conductor, and a second contactsection that is connected to the first contact section and that theelectrical coupling device engages electrically. The second contactsections of the two short-circuit devices form in each case a conductorelement in the shape of a segment of a circle, which in each case isarranged essentially at a distance r about the electrical conductor,where both second contact sections are arranged essentiallydiametrically opposite to each other.

The circumference of each second contact section is less than πr.

In this embodiment example, the electrical element can again be aconductive housing, which at least partially surrounds the conductor andthe short-circuit device.

In the mentioned example, the coupling device can present a rotatableelectrically conducting setting element with two contact elements, whereone contact element engages at a settable contact position on the secondcontact section of the first short-circuit device, and the other contactelement engages at a settable contact position on the second contactsection of the other short-circuit device. A slot is advantageouslyprovided in the housing for shifting the contact elements with the aidof the setting element, where the setting element is in electricalcontact with the housing and thus at the housing potential.

A more flexible and better performing coupling device presents a firstand a second rotatable electrically conductive setting element, eachwith a contact element, where the setting elements are movableindependently of each other. The contact element of the first settingelement engages at a settable contact position on the second contactsection of the first short-circuit device, while the contact element ofthe second setting element engages at a settable contact position on thesecond contact section of the other short-circuit device. Again, atleast one slot can be provided in the housing to move the contactelements by means of the setting element, where the setting elements areapplied against the housing, so that the setting elements and thehousing are at the same potential.

In a preferred embodiment, the contact elements are designed as slidingcontacts.

Instead of using a movable design for the coupling device, andconnecting the short-circuit device firmly to the conductor, it isconceivable to use a stationary design of the coupling device, and toattach the at least one short-circuit device in a movable way. In apossible embodiment variant, the short-circuit devices can be connectedin a freely movable way to the electrical conductor, where an electricalconnection must be guaranteed. Furthermore, the short-circuit device maybe connected to a dielectric setting element, which is applied in amovable way to the housing.

In an additional embodiment, it is conceivable not to design thecoupling device so that it is rotatable about the conductor. Instead,the coupling device could be designed so that it is movable axially withrespect to the conductor, where, in this case, the at least oneshort-circuit device runs at least section-wise parallel to theconductor, and the coupling device engages with the short-circuitdevice.

The invention will be explained in greater detail below with referenceto two embodiment examples in connection with the drawings in theappendix.

In the drawings:

FIG. 1 shows a tunable λ/4-filter subassembly according to the inventionin longitudinal cross section,

FIG. 2 shows a cross section of the λ/4-filter subassembly representedin FIG. 1,

FIG. 3 shows a side view of the λ/4-filter subassembly shown in FIG. 1,

FIG. 4 shows an alternative embodiment of a tunable λ/4-filtersubassembly according to the invention,

FIG. 5 shows a cross section of the λ/4-filter subassembly shown in FIG.4, and

FIG. 6 shows the curve plots for the VSWR for a filter subassembly withone short-circuit device and with two short-circuit devices,respectively.

FIG. 1 shows, as an example, a λ/4-filter component 10, whose centerfrequency and thus whose bandwidth is settable with the aid of twoshort-circuit devices 40 and 50 of variable length. The λ/4-filtersubassembly 10, which is represented schematically in longitudinal crosssection, presents an inner signal-conducting conductor 20, which hasconnections 25 at both of its ends. The electrical conductor 20 is heldpreferably in a central position in an electrically conductive housing30. In this example, the housing 30 has a circular cross section, wherethe diameter in the vicinity of the two line ends is less than in themiddle area of the electrical conductor 20. The two short-circuitdevices 40 and 50, for example, are soldered to the electrical conductor20, whose design is represented in greater detail in FIG. 2. In order tovary the center frequency, a coupling device 70 is provided that has twoelectrically conductive rings 73 and 75 as setting elements. Theelectrical housing can have two parallel grooves in which the rings areguided in a rotatable way. A sliding contact 72 is shaped on the ring73, which is in electrical contact with the short-circuit device 40,while on the ring 75, a sliding contact 77 is formed that is inelectrical connection with the short-circuit device 50. Slots areprovided in the housing 30, so that the sliding contacts can be movedalong the given short-circuit device by means of the rings.

FIG. 2 shows a cross section of the filter subassembly 10 andparticularly of electrically conductive housing 30, which at leastpartially surrounds the electrical conductor 20 and the twoshort-circuit devices 40 and 50. The short-circuit device 40 has a firstwire-like contact section 40 a, whose end is electrically connected at apredetermined location to the electrical conductor 20. The wire-likecontact section 40 a extends perpendicularly away from the electricalconductor 20 a contact section 40 b in the shape of a segment of acircle is formed and has a length r. on the outside end of the contactsection 40 a. The electrical conductor 20 forms the mid-point of thecontact section 40 b in the shape of a segment of a circle, where theradius of curvature of the contact section 40 b essentially correspondsto the length r. The sliding contact 72 of the annular setting element73 engages at a contact position 80 on the contact section 40 b in theshape of a segment of a circle. In the case of one rotation of theannular setting element 73, the sliding contact 72 moves along thecontact section 40 b in the shape of a segment of a circle, whichresults in the possibility of continuously changing the contact position80 and thus the length of the short-circuit device 40. The short-circuitconnection extends from the conductor 20, via the contact sections 40 aand 40 b, the contact position 80, the sliding contact 72, and thesetting element 73, to the electrically conductive housing 30.

The second short-circuit device 50 represented in FIG. 2 has a structuresimilar to the short-circuit device 40. A wire-like contact section 50 ais electrically connected to the electrical conductor 20 at a location,so that both short-circuit devices 40 and 50 lie in the same plane. Thewire-like contact section 50 a again extends perpendicularly away fromthe electrical conductor 20. A contact section 50 b in the shape of asegment of a circle is formed on its outside end. The wire-like contactsection 50 a may, if necessary, have the same length r as the wire-likecontact section 40 a. As shown in FIG. 2, both contact sections 40 b and50 b in the shape of a segment of a circle have a circumference which isless [than] πr. In this way, a setting angle of less than 180° isobtained for the setting elements 73 and 75. In the examples shown, thesetting angle can be, for example, 150°.

The sliding contact 77 of the setting element 75 engages at variablechangeable contact position 85 on the contact section 50 b in the shapeof a segment of a circle, so that the length of the short-circuit device50 can be set.

It should be noted here that the contact sections 40 b and 50 b in theshape of a segment of a circle, represented in FIG. 2, may also bedesigned as linear contact sections that are arranged parallel to theconductor 20. In this case, the setting elements 73 and 75 are notdesigned as rotatable rings, but as setting elements that can be shiftedalong the electrical conductor, where in this case, the sliding contacts72 and 75 engage at the longitudinally shaped contact sections, that runparallel to the electrical conductor.

FIG. 3 shows a top view of the filter subassembly 10 shown in FIG. 1,with the two annular setting elements 73 and 75, where markings orlocating points can be provided on the housing 30 to allow the settingof predefined bandwidths for the λ/4-filter subassembly 10.

FIG. 4 shows an alternative λ/4-filter subassembly 100, in which twoshort-circuit devices 140 and 150 are arranged with axial offset withrespect to an electrical conductor 120, and thus form a parallelcircuit. An electrical housing 130 is at least partially arranged aboutthe electrical conductor 120 and the short-circuit devices 140 and 150,and has a shape similar to that of the electrical housing 30 accordingto FIG. 1. A coupling device 170 is provided, which, with respect to theconductor 120, comprises two mutually axially offset annular settingelements 173 and 125. The annular setting element 173 has a slidingcontact 172, which engages with the short-circuit device 140 to changeits length, while a sliding contact 177 of the annular setting element175 engages with the short-circuit device 150.

FIG. 5 is a schematic representation of the cross section of the filtersubassembly 100 shown in FIG. 4. The electrical housing 130 withcircular cross section surrounds the electrical conductor 120 as well asthe short-circuit devices 140 and 150, which is electrically connectedto the conductor 130. In FIG. 5, only the short-circuit device 140 isshown. The short-circuit device 150 has a shape similar to that of theshort-circuit device 140 and is covered by the latter in therepresentation shown. The short-circuit device 140 has a wire-likecontact section 140 a, which is soldered, for example, at the contactposition of the electrical conductor 120. The wire-like contact section140 a extends perpendicularly away from the electrical conductor 120.The length of the section 140 a is r. A circular contact section 140 bis connected to the outside end of the wire-like contact section 140 aand runs essentially concentrically to and at a distance r from theelectrical conductor 120. The circumference of the circular contactsection 140 b is less than 2 πr, so that the resulting setting angle forthe setting element 173 is less than 360° but greater than the settingangle of the setting elements shown in FIGS. 1 and 2.

As shown in FIG. 5, the sliding contact 172 of the setting element 173engages at a contact position 180 on the circular contact section 140 b,resulting in the formation of an electrical connection between theelectrical conductor 120 and the housing 130, which is formed via thecontact section 140 a, the circular contact section 140 b, the slidingcontact 172 of the electrically conducting setting element 173, and thehousing 130. At an axial separation with respect to the latter, thesetting element 175 and the short-circuit device 150 are arranged. Thesetting element 173 and the setting element 175 can be movedindependently of each other, so that the bandwidth of the λ/4-filtersubassembly 10 can be varied and set.

FIG. 6 shows the curve plots of the VSWR (Voltage Standing Wave Ratio)vs frequency for a λ/4-filter with a single short-circuit device and forthe λ/4-filter subassembly shown in FIG. 4 with a parallel circuit oftwo short-circuit devices. It is evident that the bandwidth of aλ/4-filter subassembly, as shown in FIG. 4, presents a greater bandwidththan a λ/4-filter subassembly that uses only a single short-circuitdevice. The reason for this is that the two short-circuit devices 140and 150 in each case establish a center frequency for the λ/4-filter, ascan be seen in FIG. 6 at the locations labeled 1 and 2.

1. Tunable λ/4-filter subassembly (10; 100) comprising: asignal-conducting electrical conductor (20; 120), an electricallyconductive element (30; 130) that is at a reference potential, at leastone short-circuit device (40; 140) that is in electrical contact withthe electrical conductor (20; 120), and an electrical coupling device(70; 170) that couples the short-circuit device (40; 140) at a settablecontact position (80; 180) to the electrically conductive element (30;130), wherein the electrical coupling device (70; 170) and theshort-circuit device (40; 140) are movable relative to each other, sothat the length of the short-circuit device (40; 140) can be set. 2.Tunable λ/4-filter subassembly according to claim 1, characterized inthat the short-circuit device (40; 140) has a first contact section (40a; 140 a) that is connected to the electrical conductor (20; 120), and asecond contact section (40 b; 140 b) that is connected to the firstcontact section (40 a; 140 a) and that the electrical coupling device(70; 170) engages electrically.
 3. Tunable λ/4-filter subassemblyaccording to claim 2, characterized in that the second contact section(40 b; 140 b) forms an essentially circular conductor element that isarranged concentrically to and at a distance r from the electricalconductor (120) and whose circumference is less than 2 πr.
 4. Tunableλ/4-filter subassembly according to claim 1, characterized in that theelectrical element is a housing (30; 130) that at least partiallysurrounds the conductor (20; 120) and the at least one short-circuitdevice (40; 140).
 5. Tunable λ/4-filter subassembly according to claim4, characterized in that the coupling device (70; 170) has a firstrotatable electrically conductive setting element (73; 173) with acontact element (72; 172) that engages at a settable contact position(80; 180) on the short-circuit device (40; 140), wherein a slot isprovided in the housing (30; 130) to allow the passage of the contactelement, and the setting element (73; 173) is applied against thehousing (30; 130).
 6. Tunable λ/4-filter subassembly according to claim1, characterized by at least one additional short-circuit device (150)that is axially offset opposite the first short-circuit device (140),and a first contact section that is connected to the electricalconductor (120), and a second contact section that is connected to thefirst contact section and that the coupling device (170) engageselectrically.
 7. Tunable λ/4-filter subassembly according to claim 6,characterized in that the second contact section of the additionalshort-circuit device forms a circular conductor element that is arrangedconcentrically to and at a distance from the electrical conductor (120)and whose circumference is less than 2 πr, in that the electricalelement is a housing (130) that at least partially surrounds theconductor and the short-circuit devices, in that the coupling devicepresents a second rotatable, electrically conductive setting element(175) with a contact element (177) that engages at a settable contactposition with the additional short-circuit device (150), wherein a slotis provided in the housing to allow the passage of the contact element(177), and the setting element is applied against the housing (130). 8.Tunable λ/4-filter subassembly according to claim 7, characterized inthat the two setting elements (173, 175) are connected to each other orare movable independently of each other.
 9. Tunable λ/4-filtersubassembly according to claim 2, characterized by an additionalshort-circuit device (50) that presents a first contact section (50 a)that is connected to the electrical conductor (20), and a second contactsection (50 b) that is connected to the first contact section (50 a) andthat the electrical coupling device (70) engages electrically, whereinthe two short-circuit devices lie in the same plane.
 10. Tunableλ/4-filter subassembly according to claim 9, characterized in that thetwo contact sections (40 b, 50 b) of the two short-circuit devices (40,50) each form a conductor element in the shape of a segment of a circle,which in each case is arranged at a distance r about the electricalconductor (20), and in that the second contact sections (40 b, 50 b) arearranged essentially diametrically opposite to each other.
 11. Tunableλ/4-filter subassembly according to claim 10, characterized in that thecircumference of each second contact section (40 b, 50 b) is less thanπr.
 12. Tunable λ/4-filter subassembly according to claim 10,characterized in that the electrical element is a housing (30) that atleast partially surrounds the conductor (20) and the short-circuitdevices (40, 50), in that the coupling device (70) presents a rotatable,electrically conductive setting element with two contact elements,wherein one contact element engages at a settable contact position (80)on the second contact section (40 b) of the first short-circuit device(40), and the other contact element engages at a settable contactposition (85) on the second contact section (50 b) of the othershort-circuit device (50), and wherein a slot is provided in the housingto allow the passage of the contact element, and the setting element isapplied against the housing (30).
 13. Tunable λ/4-filter subassemblyaccording to claim 10, characterized in that the electrical element is ahousing (30) that at least partially surrounds the conductor (20) andthe short-circuit devices (40, 50), in that the coupling device (70)presents a first and a second rotatable, electrically conductive settingelement (73, 75), each with a contact element (72, 77), wherein thecontact element (72) of the first setting element engages at a settablecontact position (80) on the second contact section (40 b) of the firstshort-circuit device (40), and the contact element (77) of the secondsetting element (75) engages at a settable contact position (85) on thesecond contact section (50 b) of the other short-circuit device (50),and wherein at least one slot is provided in the housing (30) to allowthe passage of the contact elements (72, 77), and the setting elementsare applied against the housing (30).
 14. Tunable λ/4-filter subassemblyaccording to claim 1, characterized in that the contact elements (72,77; 172, 177) are sliding contacts.
 15. Tunable λ/4-filter subassemblyaccording to claim 1, characterized in that the at least oneshort-circuit device is attached in a movable way.
 16. Tunableλ/4-filter subassembly according to claim 1, characterized in that thecoupling device (70; 170) is movable axially with respect to theconductor (30; 130), where the at least one short-circuit device (40;50) runs parallel at least section-wise to the conductor (30).